Implementations of the claimed invention generally may relate to schemes for interpolating between frames of video information and, more particularly, to such schemes that involve motion compensation.
Frame rate conversion, which may also be referred to as temporal rate conversion, scan rate conversion or field rate conversion, may be considered a technique to convert between difference frame rates. A frame rate may be defined as number of frames displayed in a unit of time. Frame rate conversion may be desirable, for example, when exchanging video material internationally. In one particular case, video material in PAL format, which has a frame rate of 50 fields per second, may be desired in NTSC format, which has a frame rate of 60 fields per second. Thus, in order to broadcast video material recorded in PAL format in the United States, which uses NTSC format, frame rate conversion may be needed.
In addition to format conversion, or alternately, frame rate conversion can also be used to enhance perceived quality in video display systems. Differences in display refresh rates may be perceivable to human eyes, and consumers generally prefer a higher refresh rate such as 100 Hz or 120 Hz to the normal frame rate 50/60 Hz supported by broadcasting systems. Frame rate conversion capability in a video display system may enable a user of such system to watch video material at a high frame rate and better perceived quality.
To further introduce the concept of frame rate conversion, an interpolation example will be discussed with regard to FIG. 1. A video sequence 100 may include a temporal sequence of images, or frames, of which an (N−1)th frame 110 and a following Nth frame 130 are shown. A frame rate of sequence 100 may be changed, for example, by inserting an interpolated frame (or “target frame”) 120 between frames 110 and 130, with or without dropping existing frames in sequence 100. For example, if an integer multiple of the current frame rate (e.g., double, triple, etc.) is desired, one or more interpolated frames 120 may be inserted roughly equally spaced in time between existing frames 110 and 130. If another frame rate conversion factor is desired, however, interpolated/target frame 120 may be inserted closer in time to one of frames 110 and 130, possibly in conjunction with dropping pre-existing frames in sequence 100.
There are three major types of frame rate conversion schemes available: 1) frame duplicate/drop, 2) temporal interpolation, and 3) motion compensated schemes. The frame duplication/dropping may be the most widely used technique because of its simplicity to implement, but it may also provide the lowest image quality. The motion compensated schemes are generally considered as having the highest image quality, but such schemes also typically entail a high complexity in implementation. As a result of such complexity, motion compensated frame rate conversion schemes may only be available in professional equipment or very high end television or video processors.
Even such complex equipment, however, may still exhibit visual artifacts, such as “halo” artifacts, from inaccuracies in the motion compensation.